Just the kind of talk you might expect from a little guy - Taylor Stitch was founded in 2008 as a custom shirting outfit by three East Coasters in their early 20s - about to take a few cuts in the big leagues.

On Tuesday, Taylor Stitch unveils its latest collection of made-in-San Francisco men's custom and ready-to-wear shirts not on the caffeine-fueled stretch of Valencia Street it calls home (383 Valencia St.) but in the Grant Avenue flagship store of clothier Banana Republic for the next 18 weeks.

But if the two brands are operating at different ends of the market - Banana as a mass-market retailer selling foreign-made goods at fantastic scale, and Taylor Stitch the scrappy upstart selling small batches of sewn-in-SoMa button-downs to creative types for $125 a pop - the two companies find common ground in their local origins.

"We love the idea of celebrating our roots here in San Francisco," said Milo Slattery, the vice president of men's merchandising at Banana Republic, adding that the two companies were a natural fit because they both "champion American sportswear."

"Gap was founded here by the Fisher family," he said, "and when we saw what Taylor Stitch was doing, we loved their product and that their story is similar to ours." Banana Republic launched in Mill Valley in 1978, the safari-inspired product of Mel and Patricia Ziegler (both former Chronicle employees), eventually selling to Gap Inc. in 1983.

Taylor Stitch was founded by Maher, 27, and Barrett Purdum, 27, pals from Babson College outside Boston (Babson also claims menswear designer of the minute Michael Bastian as an alum). After moving to San Francisco to start their custom shirting business, they added Michael Armenta, 26, to the team, working out of the apartment Maher and Purdum shared.

Taylor Stitch spent about a year on Mission Street as the flagship brand of the trio's event-cum-retail-space the Common and finally landed on Valencia Street last year. But with the renovation of a new office space on South Van Ness under way, a buzzing online presence and the summertime launch of a small women's collection, Taylor Stitch is hitting its stride. And the local young Turks are taking notice.

Banana Republic made a recent splash with its "Mad Men" collection, a nationwide bid at mid-century cool, but Taylor Stitch's 10 off-the-peg shirts and 250 fabrics for custom shirting are a flagship-only affair. And you'll find the collaboration's shop within a shop in a three-walled installation the host designed in conjunction with Armenta on the main men's floor starting this Tuesday.

Though the ready-to-wear shirts don't deviate aesthetically from Taylor Stitch's primary aim - smart, locally made, trim-fitting basics - Slattery believes that the Banana Republic customer will jump at Taylor Stitch's custom shirting expertise. So much so that the T.S. team spent hours training Banana's sales associates in how to take the nine measurements necessary to work out a quality custom job.

Big brands partnering with smaller manufacturers is hardly news these days - J. Crew has been teaming up with menswear catnip brands like Alden, Pantherella, Barbour and the Hill-Side for years - but Maher says this match wasn't made in some far-off marketing department.

Instead, he describes how Tom Girard, senior men's merchandiser at Banana Republic, came into Taylor Stitch at the end of last year and loved what he saw. "He made us his pet project, and then proposed a shop within a shop around Christmastime," he said.

Those worried that a call up to the majors might add a bit of undue gloss to Taylor Stitch's rugged, unfussy appeal should be assured that what Maher calls his "matte-finished brand" isn't after any mass-market slickness. For him, it's always about the story that he's telling through his clothes. And this one seems to be about a clothing giant giving a leg up to a local comrade.